1. In Jaimini astrology, the calculation of degrees, minutes and seconds of all the planets should be done properly.
2. Write all the seven planets in the descending order based on their degrees and make a table. If the degrees and minutes of planets are equal then you should see the value of planet till seconds and decide the order of planets.
3. The planet with highest degrees should be written on the top of the table. After that, the planet with lesser degrees should be written and similarly, all other planets should be arranged.
4. The planet with highest degrees is called Atmakaraka.
5. The planet after that is called Amatyakaraka.
6. The planet with lesser degrees than Amatyakaraka is called Bhratrikaraka.
7. The planet with lesser degrees than Bhratrikaraka is called Matrikaraka.
8. The planet after Matrikaraka is called Putrakaraka.
9. The planet with lesser degrees than Putrakaraka is called Gyatikaraka.
10. The planet with lowest degrees is called Darakaraka.

Here is an example Kundali for you:
Birth details are:
Birth Date:19/02/1998
Birth Time: 15:40Hours
Birth Place: Delhi

You can use this link to prepare the Kundali on Astrobix.com. In this Kundali, according to the degrees of planets, Karakas are as follows:

Sun-06degrees-43minutes-07seconds
Moon-04degrees-08minutes-38seconds
Mars-25degrees-50minutes-19seconds
Mercury-04degrees-20minutes-07seconds
Jupiter-09degrees-44minutes-58seconds
Venus-27degrees-59minutes-03seconds
Saturn-23degrees-15minutes-34seconds

On the basis of above-mentioned degrees, write the planets in the descending order. You will get a table in the following way:
Atmakaraka-Venus
Amatyakaraka-Mars
Bhratrikaraka-Saturn
Matrikaraka-Jupiter
Putrakaraka-Sun
Gyatikaraka-Mercury
Darakaraka-Moon

Mercury and Moon have same degrees in the Kundali. Therefore, we compared minutes of the two planets. The minutes of Mercury are greater than the minutes of Moon, therefore, Mercury becomes Gyatikaraka and Moon becomes Darakaraka.